The present invention relates to hydraulic or pneumatic actuators such as linear cylinders, and is more particularly directed to a pressure-balanced rod seal which prevents or limits external leakage where the rod extends through a pressure barrier, but which avoids the high friction that often accompanies pressure actuated rod seals.
Several types of seals are energized by the pressure that they are intended to control. This pressure energization produces a radial force on the seal. The radial force causes seal wear, and decreases the seal life. This requires frequent cylinder refurbishments. In addition, radial force from the pressurized seal is often the main source of friction in the cylinder.
Hydraulic or pneumatic cylinders that are used for specialized service, such as in flight simulators or flying shears, often employ hydrostatic bearings to improve bearing life and friction characteristics. However, these bearings are quite elaborate and are costly to produce, but still produce significant leakage which adds to the hydraulic power requirements.